In full-duplex systems, such as Gigabit Ethernets and others, the system must be capable of transmitting and receiving signals on a same differential pair wire. Due to the large signal swings in the channel (transmitted signal plus the received signal), it is highly desirable to reject the echo signal (near-end transmit signal) as much as possible, leaving more room for the received signal, thereby maximizing the dynamic range.
For a given noise in a receiver, the received signal-to-noise ratio (SNR) degrades as the signal travels through long distances, e.g., 100 meters. Hence, cable equalization along with automatic gain control circuits are used to maximize the SNR along with reducing the inter-symbol interference (ISI), thereby utilizing the entire dynamic range of the receiver. The final received signal is then digitized via an analog-to-digital converter (ADC) for further digital signal processing (DSP). These conventional systems suffer from a degrading signal-to-residual echo ratio and signal-to-noise ratio at higher cable lengths.
Therefore, there is a need in the art for an improved echo-cancellation and automatic gain control front end to reduce these problems in conventional systems.